The present invention relates to plant and process for automatically gluing polarising lenses.
More specifically, the invention relates to plant and process of the above kind allowing to obtain in a completely automatic manner a so called xe2x80x9ccoupledxe2x80x9d polarised lens (lens-film-lens) having a null power, to be used for sunglasses.
In other words, the invention allows to automatically produce polarised blanks for the subsequent production of glass lenses.
Coming now to provide as an introduction some information concerning the polarising lenses, it is well known that visible light is comprised of electromagnetic waves, having a wavelength approximately between 380 and 780 nm.
Other features of the luminous radiations are the radiation intensity ad geometry of the electromagnetic wave oscillation.
As to the oscillation geometry, also known as xe2x80x9cpolarisationxe2x80x9d, it can occur according to randomly oriented planes, also known as xe2x80x9crandom polarisationxe2x80x9d or xe2x80x9cnon polarisedxe2x80x9d, or according to a single plane (xe2x80x9clinear polarisationxe2x80x9d), i.e. within a cylindrical surface (xe2x80x9ccircular polarisationxe2x80x9d).
Naturally, light usually is not polarised. Reflection on reflecting surfaces (glazed doors, water surfaces, snow or ice surfaces, bright or wet asphalt) and having suitable angles, produces a certain degree of polarisation.
The effect is that of a glow coming from the zone of the surface where the polarised reflection is maximum. A remarkable inconvenience for the view is caused by the strong reflection. For example, this effect, on the water surfaces, prevents the vision under the water surface.
Polarising lenses are able to filter direct light as a standard xe2x80x9csunxe2x80x9d lens and to eliminate (according to a certain degree of efficiency, polarised reflected light which is particularly troublesome.
Main comfort is the elimination of the fastidious reflexes normally present on the glazed doors, water mirrors, iced surfaces and asphalted roads.
Glasses polarised lenses are usually comprised of two thin lenses between which the polarising film is interposed.
Lenses and film are coupled by an adhesive placed on both faces of the film, thus realising an assembly having five layers:
outer or xe2x80x9cconvexxe2x80x9d lens;
glue;
polarising film;
glue;
inner or xe2x80x9cconcavexe2x80x9d lensxe2x80x9d.
Additional outer or inner layers can be comprised of surface treatments to confer to the lenses particular esthetical or mechanical properties.
Optical properties of the whole assembled lens depends on the properties of the single layers and also on the geometrical regularity of the assembling phase. A uneven amount of glue, or non-parallelism among the different layers, produces optical effects not acceptable for the finished product (aberrations, distortions and optical definition loss).
The known assembling technique provides the use of preformed film (i.e. already curved by the manufacturer) and then the manual gluing after having applied the adhesive on both the film surfaces.
Then, adhesive is catalysed by UV lamps.
It can be easily understood that such a process does not ensure concentricity of filtering and transparent layers and thus of the liquid layers (adhesive) before the catalysation, with the consequent above mentioned optical defects.
Manual assembling operations are very expensive since they require a very long time and they must be carried out paying a great care by skilled personnel to avoid and eliminate air bubbles produced during the approaching of the lenses to the adhesive and already present on the same adhesive.
This kind of solution is shown for exemplificative purposes in FIG. 1a. 
Up to date, the Applicant has privileged the production of glass polarising lenses, since the precision and geometrical stability of the lenses which are optically worked are preferred.
Generally speaking, technology employed until today to glue the lenses provides the shaping of the polarised film by different methods and then the manual gluing after having placed the adhesive on the two film surfaces.
Afterwards, catalysation of the adhesive is carried out by UV lamps.
Process according to the prior art does not ensure the concentricity of the filtering and transparent layers and thus the thickness of the liquid layers (adhesive), before catalysation.
Consequently, a series of optical defects occur such as aberrations, distortions and optical definition loss.
It is well evident that manual assembling operations are very expensive since they require a very long time and they must be carried out paying a great care by skilled personnel to avoid and eliminate air bubbles produced during the approaching of the lenses to the adhesive and already present on the same adhesive.
Main object of the present invention is that of solving the above mentioned drawbacks characteristic of the manual workings.
Particularly, the solution according to the present invention allows to obtain a high optical precision of the spherical surfaces comprising the lens, thus eliminating defects (air bubbles, ecc.).
Furthermore, the invention avoids any risk of low productivity, or in any case the need of a high number of personnel, being the process completely automated, and allows to obtain a high productive repetitiveness and a remarkable average quality standard.
These and other results are obtained according to the invention, providing improvement in the under vacuum application and shaping of the polarising film, in the prism, optical definition and aberration defects elimination, by the control of the curvature rays and of the thickness of the five layers comprising the lens, and by the realisation of a completely automatic plant for the realisation of the lens starting from blanks (lenses and polarising film).
It is therefore specific object of the present invention a plant for the continuous production of polarising lenses, comprising a coil polarising film feeding station; a glass convex lens feeding station; a concave lens feeding station; an under vacuum film shaping station on spherical moulds; a deposition and gluing outer convex lens station; a translation station for the pre-glued lenses; a deposition and gluing inner concave lens station; a lens separation and film cutting station; and a palletisation station for the finished lenses, said plant functioning automatically.
In a preferred embodiment of the plant according to the present invention said concave and convex lens deposition and gluing stations provide an approaching motion of the lens to the glue bead in such a way to realise a substantially point contact between lens and glue, without air trapping.
Preferably, according to the invention, the lens is approached to the bead with its axis not coinciding and after the contact a diagonal motion of the lens is realised until centring the same, followed by a slight vertical pressure to preliminarily spread the glue.
Still according to the invention, after said vertical pressure a spiral or circular rotatory motion can be carried out to further spread the and to homogenise the glue.
Preferably, according to the invention, said film fed on a coil is provided on a protection support, in said coil film feeding station a collection coil for the protection support being provided.
Furthermore, according to the invention, downward said glass convex lens feeding station an orienteering station is provided (to apply oriented coatings, such as degrading coatings, or for use with de-centred lenses, wherein optical centre does not coincide with the geometrical centre).
Always according to the invention, upward the palletisation station a marking section to mark the polarisation axis can be provided.
Furthermore, according to the invention, a washing station can be provided, wherein thin lenses to be glued can be washed by an automatic apparatus, employing suitable detergents, ultrasounds, rinsing by demineralised and osmotised water.
Still according to the invention, said washing station can be connected in correspondence of its end part where the washed lenses are returned, with the concave and convex lens feeding stations.
Preferably, according to the invention, two separate washing stations are provided, respectively for the inner and the outer lenses, for example employing two automatic washing machines (mainly in case of direct connection with the relevant charging station of the original gluing apparatus), or with a single automatic washing machine alternatively used for the two washings.
It is well evident that the automatic washing before the gluing phase is very important since it avoids to obtain defective finished lenses that cannot be recovered, due to the presence of impurties within the layers, caused to a not complete washing or to a subsequent deposit of dust, in case the lenses are washed in a separate apparatus.
Furthermore, according to the invention, the washing station and the gluing station are closed within a depulverised room, which is provided with a laminar air flow with absolute filters.
Always according to the invention, the finished product can be subjected to a washing in another automatic apparatus, preferably equal to the apparatus employed to wash the lenses to be glued, provided at the exit of the same gluing apparatus.
Automatic washing after gluing is very important since it eliminates the glue residuals (that as oleos residuals can contaminate also the lens surfaces), generally due to the dirtying of the mechanical parts of the gluing apparatus during the normal continuative work.
This washing station too, along with the other parts of the plant, can be closed within a depulverised room provided with laminar air flow with absolute filters.
Always according to the invention, it can be provided a testing station in order to be possible to test the finished lenses to verify cosmetic defects of any kind.
Said operation is important to reveal eventual defects induced by the same gluing phase, such as air bubbles and polarising film defects (impurities, holes or tears, plies).
Preferably, said operation is carried out by the integration of an automatic system, at the end of the gluing apparatus, said system employing artificial vision.
To this end, it is necessary the contemporaneous use of the automatic washing system, interposed between gluing and testing apparatuses.
In order to improve the uniformity of the glue layer between lens and film, on one or both the lenses, the application of a pressure on all or part of the lens surface, by a curved plug, can be provided during the gluing phase.
In this way, forcing the spreading of the glue, a better geometrical regularity of the layer and thus better optical performances of the finished coupled lens, is reached.
Furthermore, according to the invention, in order to confer to the finished lens particular features, polarising film having one or more of the following further properties can be used:
UV-blocking, i.e. a transmission close to 0% of UV radiation up to 400 nm;
high efficiency, i.e. high difference of the absorbency of polarised film when the film is perpendicular to the polarisation direction with respect to when it is parallel to the polarisation direction;
black-crossing, i.e. minimum variation of the colour tone of the polarised light when the film is perpendicular to the polarisation direction, with respect to when it is parallel to the polarisation direction.
Furthermore, according to the invention, in order to confer to the finished lens particular features, adhesive having one or more of the following further properties can be used:
UV-blocking, i.e. a transmission close to 0% of UV radiation;
high protection of the film with respect to the ageing and decolorisation (feature mainly connected to the UV absorption, since glue surrounds the film on the two surface);
high resistance to the impact breaking, in such a way to be able to easily satisfy the resistance requisites provided by the international rules;
high resistance to the delamination, i.e. better adhesiveness to the glass and film surfaces, in such a way to withstand to the outer physical-chemical agents aggression (such as humid and/or hot atmosphere, salted atmospheres, ecc.);
catalysation capability at a higher wavelength (particularly beyond UV), in such a way to be catalysed by broad spectrum UV blocking lamps (such as some kinds of polarising films and some kinds of glass and coating).
Always according to the invention, in order to allow the catalysation also in case of presence of layers blocking UV (such as some polarising films and some kinds of glass and coating), it is possible to use lamps having a broad emission spectrum, preferably combined with special adhesives.
It is further specific object of the present invention a process for the production of polarising lenses, comprising the steps of:
feeding polarising film from a coil;
feeding convex lenses;
feeding concave lenses;
under vacuum shaping the film on spherical moulds;
depositing and gluing the outer convex lenses;
translating the pre-glued lenses;
depose and gluing the inner concave lenses;
separating the lenses and eliminating the exceeding film from the single lenses;
palletsing the finished polarising lenses,
all the steps of the process being performed automatically.
Preferably, according to the invention, said concave and convex lens deposition and gluing phases provide an approaching motion of the lens to the glue bead in such a way to realise a substantially point contact between lens and glue, with a coupling speed in function of the surface tension of the bead such as not to allow that the expansion front of the bead closes thus trapping air.
Always according to the invention, the lens is preferably approached to the bead with its axis not coinciding and after the contact a diagonal motion of the lens is realised until centring the same, followed by a slight vertical pressure to preliminarily spread the glue.
Still according to the invention, after said vertical pressure a spiral or circular rotatory motion can be carried out to further spread the and to homogenise the glue.
Furthermore, according to the invention, said film fed on a coil can be provided on a protection support to collected, when separated by a suitable coil.
Still according to the invention, said process can provide downward said glass convex lens feeding station an orienteering phase (to apply oriented coatings, such as degrading coatings, or for use with de-centred lenses, wherein optical centre does not coincide with the geometrical centre).
Always according to the invention, upward the palletisation station a marking phase to mark the polarisation axis can be provided.
Furthermore, according to the invention, a washing phase of the lenses to be glued and a washing phase of the final product can be provided.
Still according to the invention, an automatic testing phase of the finished product can be provided.
Always according to the invention, during said gluing phase the application of pressure on allow only on part of the surface of the lens can be provided.
Furthermore, according to the invention, in order to confer to the finished lens particular features, polarising film having one or more of the following further properties can be used:
UV-blocking, i.e. a transmission close to 0% of UV radiation up to 400 nm;
high efficiency, i.e. high difference of the absorbency of polarised film when the film is perpendicular to the polarisation direction with respect to when it is parallel to the polarisation direction;
black-crossing, i.e. minimum variation of the colour tone of the polarised light when the film is perpendicular to the polarisation direction, with respect to when it is parallel to the polarisation direction.
Furthermore, in order to confer to the finished lens particular features, adhesive having one or more of the following further properties can be used:
UV-blocking, i.e. a transmission close to 0% of UV radiation;
high protection of the film with respect to the ageing and decolorisation (feature mainly connected to the UV absorption, since glue surrounds the film on the two surface);
high resistance to the impact breaking, in such a way to be able to easily satisfy the resistance requisites provided by the international rules;
high resistance to the delamination, i.e. better adhesiveness to the glass and film surfaces, in such a way to withstand to the outer physical-chemical agents aggression (such as humid and/or hot atmosphere, salted atmospheres, ecc.);
catalysation capability at a higher wavelength (particularly beyond UV), in such a way to be catalysed by broad spectrum UV blocking lamps (such as some kinds of polarising films and some kinds of glass and coating).
Finally, according to the invention, in order to allow the catalysation also in case of the presence of layers blocking UV rays (such as in some kind of polarising films and some kinds of glass or coating), lamps having a broad emission spectrum, preferably combined with special adhesives, are used.